Copolymerization process



molecular weights are obtained.

United States Patent Othce 3,012,012 Patented Dec. 5, 1961 3,012,012 COPOLYMERIZATION PROCESS Richard H. Martin, Jr., Springfield, Mass, assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. F led July 31, 1959, Ser. No. 830,707 8 Claims. (Cl. 26078.5)

-The present invention relates to novel vinyl chloride iuterpolymers and to methods for preparing same.

Vinyl chloride homopolyrners are widely employed as a surface coating resin, as a wire insulation resin, and for diverse other purposes. A relatively recent development in the art has been the employment of vinyl chloride polymer insulated wires as underground electrical cables. The insulation on such underground cables must be able to withstand severe physical punishment and for maximum utility requires vinyl chloride polymers having physical properties superior to those of many of the presently commercially available vinyl chloride homopoly mers. In particular, this development requires vinyl chloride polymers having a high tensile strength, a high 100% modulus and a high crush-resistance.

It is known that the physical properties of vinyl chloride homopolymers such as tensile strength, 100% modulus and crush-resistance can be improved by preparing the polymer under such conditions that higher To obtain such higher molecular weights it has heretofore been necessary to lower the polymerization temperature or to reduce the concentration of free radical generating polymerization initiator employed or both. Such modifications of the polymerization process increase the cost of preparing vinyl chloride homopolymers in that they lower the rate of polymerization and concomitantly the productive capacity of the equipment in which the polymer is prepared.

A method sometimes proposed for increasing the molecular weight of polymers is to incorporate a small quantity of a cross-linking monomer, i.e., a monomer containing two or more non-conjugated terminal ethylenic groups, in the monomer charge. This method has been used successfully with some polymer systems, but it is not generally applicable to the preparation of vinyl chloride polymers of high molecular weight. In particular, it is difilcult to find cross-linking monomers which will interpolymerize with vinyl chloride at satisfactory rates. Moreover, where interpolymers can be formed, they tend to be quite heterogeneous in composition and in most cases the interpolymer contains a highly gelled fraction which is insoluble in most solvents for the vinyl chloride interpolymer. Such interpolymers, because of their heterogeneity and insoluble gel fraction, can not be employed in surface coating compositions.

It is an object of this invention to provide vinyl chloride polymers having improved physical properties.

Another object of this invention is to provide a proccss for preparing vinyl chloride polymers of improved physical properties, which process can be carried out in conventional polymerization equipment.

A further object of this invention is to provide a vinyl chloride polymerization process which, with no sacrifice in the rate of polymerization, yields vinyl chloride polymers of improved physical properties.

Other objects and advantages of this invention will be apparent from the following detailed description thereof.

It has been discovered that vinyl chloride polymers of improved physical properties, as compared with vinyl chloride homopolymers prepared under otherwise identical conditions, can be obtained by interpolymerizing minute but critical quantities of an alkylene glycol bisallylmaleate or an alkylene glycol bisallylfumarate with vinyl chloride. Such improved vinyl chloride interpolymers contain 0002-005 weight percent of the alkylene glycol bisallylmaleate with the balance of the interpolyrner being vinyl chloride. The vinyl chloride interpolymers of improved physical properties are obtained at rates of polymerization which are fully equivalent to those obtained in the homopolymerization of vinyl chloride.

As noted earlier herein, it is known that the physical properties of vinyl chloride polymers such as tensile strength, modulus and crush-resistance are improved as the molecular weight of the vinyl chloride polymer is increased. This is true not only for vinyl chloride polymers per se, but also for formulated vinyl chloride polymer compositions containing plasticizers, pigments, fillers and other conventional polymer compounding ingredients. Since the precision of molecular weight determinations is much higher than the precision of determinations of tensile strength, 100% modulus and crush-resistance, the comparison of polymer properties in the subsequent examples is based primarily upon polymer molecular Weights, such molecular weights being expressed in terms of the specific viscosities of the polymers. All of the specific viscosities reported herein are determined on 0.4 weight percent solutions of the polyme: in cyclohexanone at 25:0.05 C. The precision of the reported values is $0.002. The formula employed for calculating specific viscosities is set forth below:

Solution viscositysolvent viscosity Specific viscosity:

Solvent viscosity The following examples are set forth to illustrate more clearly the principle and practice of this invention to those skilled in the art. All parts are by weight.

EXAMPLE I Part A A vinyl chloride homop'olymer is prepared me stirred autoclave employing the suspension polymerization system set forth below:

Component: Parts by weight Monomer '100 Water suspending agent 1 0.15 Lauroyl peroxide 0.25

Equimolar lnterpolymer of vinyl acetate and malelc auhydride. I

The polymerization is carried out at 51 C. and is completed in about 16 hours. The vinyl chloride homopolymer has a specific viscosity of 0.51.

Part B I polymer.

polymer contains only 0.01 weight percent of the triethylene glycol bisallylmaleate, the specific viscosity of the resulting interpolymer is about 14% higher than the value obtained with the vinyl chloride homopolymer.

Part C The vinyl chloride-triethylene glycol bisallylmaleate interpolymer of Part B is compounded into the wire coating formulation set forth below:

The resulting formulation has a tensile strength of about 2600 p.s.i. and 100% modulus of about 1800 psi. By way of contrast, when the vinyl chloride hom-opolymer of Example I, Part A, is substituted for the vinyl chloridetriethylene glycol bisallylmaleate interpolymer, the resulting formulation has a tensile strength and 100% modulus approximately 100 points lower.

EXAMPLES II-V Example I, Part B, is repeated except that the triethylene glycol bisallylmaleate contained in the polymerization systems is replaced with, respectively, triethylene glycol bisallylfumarate, ethylene glycol bisallylmaleate, propylene glycol bisallylmaleate, and hexamethylene glycol bisallylmaleate. The physical properties of the resulting interpolymers correspond to those of the interpolymer obtained in Example I, Part B.

EXAMPLES VI-X Five vinyl chloride-triethylene glycol bisallylmaleate interpolymers containing varying quantities of triethylene glycol bisallylmaleate are prepared under identical polymerization conditions following the procedure of Example I, Part B. The composition of the interpolymers and the specific viscosities thereof are set forth in Table I.

Wt. Percent Triethylene Specific Polymer Glycol Bis- Viscosity allylmaleate in Interpolymer Control-Vinyl Chloride Homopolymer 0.51 Example 0. 003 0. 53 Example VII 0. 005 0. 54 Example VIII.-. 0. 007 0.56 Example IX. 0. 015 O. 62 Example X- 0.020 O. 66

As seen from the above table, each of the interploymers containing triethylene glycol bisallylmaleate has a higher specific viscosity than the control vinyl chloride homo- Each of the triethylene glycol bisallylmaleate containing interpolymers also has a higher tensile strength and 100% modulus than the control vinyl chloride homopolymer. In addition, each of the interpolymers is free of gels and iscompletely soluble in such solvents as cyclohexanone and nitrobenzene. Accordingly, the interpolymers are well suited for use in paints and other surface coating compositions.

The interpolymers of this invention are binary interpolymers consisting of 99.95-99.998 and preferably 99.98- 99.995 weight percent of vinyl chloride and, correspond- 4 ingly, 005-0002 and preferably 0.02-0.005 weight percent of a monomer of the formula:

where alkylene is an alkylene group containing 2-6 carbon atoms, :1 has a value of 1-3 and R and R are independently selected from the group consisting of a hydrogen atom and a methyl radical.

Typical examples of monomers conforming to the above formula include, in addition to the monomers employed in the examples, diethylene glycol bisallylmaleate, diethylene glycol bisallylfumarate, dipropylene glycol bisallylmaleate, butylene glycol bisallylmaleate, dibutylene glycol bisallylmaleate, neopentyl glycol bisallylmaleate, ethylene glycol allylmaleate allylfumarate, ethylene glycol bismeth allylmaleate, etc. Such monomers can be prepared by esterifying one mol of the appropriate alkylene glycol with two mols of monoallylmaleate, monomethallylmaleate, monoallylfumarate, monomethallylfumarate or a mixture thereof employing conventional esterification procedures Which will be obvious to those skilled in the art. Certain of the above mentioned monomers are commercially available and the preparation of others are described in the chemical literature. For diverse reasons, including cost and ease of polymerization, the preferred monomers to be employed in the invention are the mono-, di-, and triethylene glycol bisallylmaleates.

The interpolymers of the invention are preferably prepared by the well-known suspension polymerization process in which the monomers are dispersed as small droplets in water and polymerized therein. Although a watersoluble interploymer of vinyl acetate and maleic anhydride has been employed as the suspending agent in the examples herein presented, other known suspending agents such as gelatine, protective colloids, etc. may be employed if desired. The polymerizations are carried out at temperatures in the range of 30-70 C. in the presence of free radical generating polymerization initiators such as lauroyl peroxide, benzoyl peroxide, etc.

The interpolymers of this invention have higher molecular weights and better physical properties than corresponding vinyl chloride homop-olymers prepared under identical polymerization conditions. Thus, the process of this invention makes possible the attainment of a su perior product at no increase in cost. Alternatively, interpolymers of this invention having equivalent physical properties to vinyl chloride homopolymers can be prepared at higher polymerization temperatures. Polymerizing the interpolymers at higher temperatures increases the rate of polymerization and raises the productive capacity of the polymerization vessel in which the reaction is carried out. Thus, the interpolymers of this invention make possible the attainment of a higher productive capacity per unit of capital investment. In general, the productive capacity of a polymerization vessel for the interpolymers of this invention is approximately 30% higher than the productive capacity of the same vessel for a vinyl chloride homopolymer, both of said polymers being polymerized under conditions which give identical molecular weights.

The interpolymers of this invention may be used interchangeably with vinyl chloride homopolymers in virtually all industrial applications. The interpolymers are particularly suitable for use in the insulation of electric wire and particularly for electric wire that is to be employed as underground cable.

The above descriptions and particularly the examples are set forth by way of illustration only. Many other variations and modifications thereof will be obvious to those skilled in the art and can be made without departing from the spirit and scope of the invention herein disclosed.

What is claimed is:

1. A resinous interpolymer of monomers consisting of 99.95-99.998 weight percent of vinyl chloride and, correspondingly, 0.05-0.002 weight percent of a monomer of the formula:

where Alkylene is an alkylene group containing 2-6 carbon atoms, n has a value of l-3 and R and R are independently selected from the group consisting of a hydrogen atom and a methyl radical.

3. A resinous interpolymer of monomers consisting of 99.98-99.995 weight percent of vinyl chloride and, correspondingly, 0.02-0.005 weight percent of triethylene glycol bisallylmaleate.

4. A resinous interpolymer of monomers consisting of 99.98-99.995 weight percent of vinyl chloride and, correspondingly, 0.02-0.005 weight percent of triethylene glycol bisallylfumarate.

5. A resinous interpolymer of monomers consisting of 99.98-99.995 weight percent of vinyl chloride and, correspondingly, 0.02-0.005 weight percent of ethylene glycol bisallylmaleate.

6. An insulated electric wire comprising an electrical conductor carrying an insulating coating of a resinous interpolymer of monomers consisting of 99.95-99.998 weight percent of vinyl chloride and, correspondingly, 0.05-0.002 weight percent of a monomer of the formula:

where Alkylene is an alkylene group containing 2-6 carbon atoms, n has a value of 1-3 and R and R are independently selected from the group consisting of a hydrogen atom and a methyl radical.

7. A suspension polymerization process for preparing a resinous interpolymer of a monomer mixture consisting of 99.95-99.998 weight percent of vinyl chloride and, correspondingly, 0.05-0.002 weight percent of a monomer of the formula:

where Alkylene is an alkylene group containing 2-6 carbon atoms, n has a value of 1-3 and R and R are independently selected from the group consisting of a hydrogen atom and a methyl radical, which process com prises dispersing the monomers as droplets in an aqueous medium containing therein a suspending agent and polymerizing the monomers at a temperature of 3070 C. in the presence of a free radical generating polymerization initiator.

8. A suspension polymerization process for preparing a resinous interpolymer of a monomer mixture consisting of 99.98-99.995 weight percent of vinyl chloride and, correspondingly, 0.02-0.005 weight percent of a monomer of the formula:

where Alkylene is an alkylene group containing 2-6 carbon atoms, n has a value of 1-3 and R and R are independently selected from the group consisting of a hydrogen atom and a methyl radical, which process comprises dispersing the monomers as droplets in an aqueous medium containing therein a suspending agent and polymerizing the monomers at a temperature of 3070 C. in the presence of a free radical generating polymerization initiator.

References Cited in the file of this patent UNITED STATES PATENTS 2,898,224 Martin Aug. 4, 1959 FOREIGN PATENTS 595,056 Great Britain Nov. 26, 1947 

1. A RESINOUS INTERPOLYMER OF MONOMERS CONSISTING OF 99.95-99.998 WEIGHT OF VINYL CHLORIDE AND, CORRESPONDINGLY 0.05-0.002 WEIGHT PERCENT OF A MONOMER OF THE FORMULA: 